Bacterial morphology is determined primarily by the architecture of the peptidoglycan (PG) cell wall, a mesh-like layer that encases the cell. that the buildup of ECA-lipid II sequesters part of the pool of Und-P, which, in turn, adversely affects PG synthesis. The data strongly suggests there is competition for a common pool of Und-P, whose proper distribution to alternate metabolic pathways is required to maintain normal cell shape in mutants lacking the fatty acid synthase FabH cannot change size in response to nutrient availability, thus implicating fatty acid biosynthesis in cell size regulation (Yao created morphological abnormalities. WecE is involved in the biosynthesis of enterobacterial common antigen (ECA), a non-essential glycolipid found in the outer membrane of mutant accumulates the ECA intermediate lipid II (ECA-lipid II), which triggers several cell envelope stress responses and confers sensitivity to bile salts (Danese by using a cell sorting assay previously employed to enrich for spontaneous shape suppressor mutants (Laubacher CS109 was mutagenized with EZTnKan-2 (Epicentre) to give a preliminary library of approximately 5,000 independent insertion mutants, which were pooled, grown in LB medium at 37C and analyzed by flow cytometry. The shape distribution of the mutant population was nearly identical to CS109 (Fig. 1A and 1B). Given this, we defined a selection gate to sort aberrantly shaped cells from the mutant population. Burke prevented AmiA and AmiC from processing PG during growth and division, causing the cells to grow as unseparated cells (Fig. 1E) (Bernhardt & de Boer, 2003, Ize gene, which encodes a TDP-4-keto-6-deoxy-D-glucose aminotransferase that is required for elongating lipid III during the synthesis of ECA (Fig. 2A) (Meier-Dieter alone, we deleted (mutant exhibited the same phenotypes as the mutant grown in LB broth revealed that cells grew longer at elevated temperature (compare 25C vs MF63 37C) and became noticeably swollen (25% MF63 wider than wild type) at 37C (Table 1). Moreover, while the growth rate of the mutant was similar to the parent strain when grown at 25C, 30C and 37C in LB broth, the mutant underwent a limited lysis shortly after being shifted to 42C before resuming growth at rate similar to that of the wild type (Fig. S1). All morphological and growth defects were rescued by expressing from a plasmid (Fig. 3A and 3B, and not shown). Figure 2 ECA is not required to maintain cell shape in shape defects Table 1 Morphological phenotypes of an mutant mutants prevent the formation of ECA-lipid III and therefore accumulate the intermediate ECA-lipid II (Fig. 2A) (Danese mutant was inhibited on LB containing 1% deoxycholate (Fig. 4A), confirming that the outer membrane was defective. Figure 4 Suppression of bile salt sensitivity ECA pathway mutants also trigger the Rcs stress response and inhibit motility (Castelli mutant, and this defect was suppressed by deleting the Rcs regulator (Fig. S2). The Cpx stress response is also stimulated in mutants and negatively regulates motility (Danese mutant, we deleted the Cpx response regulator, cmutant, but this had little effect (Fig. S2). Moreover, the migration of a mutant was indistinguishable from MF63 that of the mutant (Fig. S2). These results indicate that the Cpx stress response does not significantly alter motility in mutants. Collectively, these data indicate that is required to maintain normal cell shape and envelope integrity in cells suggested two possibilities: either ECA was required to maintain proper cell shape, or else shape defects were caused by the accumulation of ECA-lipid II. To distinguish between these alternatives, we first deleted mutant should exhibit the same phenotype as the mutant. However, cells looked normal (Fig. 2B), although the forward scattered light of the mutant population shifted slightly to the right compared to the wild type (Fig. 2C). Since neither nor cells synthesize ECA (Fig. 2A), but the cells retained their normal rod shapes, the results demonstrated that ECA itself was not required to maintain wild type morphology. This suggested that accumulation of ECA-lipid II was responsible for the shape defects in cells. If true, then deleting should reverse the shape defects caused by the mutation, because ECA-lipid II would no longer be synthesized. Consistent with this prediction, the cells of a double mutant were of normal ITGA8 shape (Fig. 2B and 2C), indicating that the accumulation of ECA-lipid II.